Conventionally, as services to set communication channels between wireless terminals, wireless direct link services providing direct linking, and wireless indirect link services providing indirect linking via a wireless access point (base station) are known. In addition, wireless communication systems capable of providing both wireless direct link services and wireless indirect link services are known.
Furthermore, a method is known for deciding which service should be selected when setting a communication channel in above-described wireless communication systems. For instance, a configuration is known in which a wireless direct link service is selected according to an instruction from the side of a wireless access point (Japanese Patent Application Laid-Open No. 2005-33536).
In addition, techniques for switching communication services during communication are known. For instance, a method is known in which switching to wireless direct link service communication may be performed during wireless indirect link service communication when a receiving-side terminal is able to receive transmitted data addressed to itself from a transmission source terminal via a base station at or above a specific level (Japanese Patent Application Laid-Open No. 2004-128785).
Furthermore, the following method is known. After completion of link authentication to a wireless system, a communication partner is first specified from a transmission source terminal using an indirect link service. Next, a test signal is directly transmitted to the partner terminal, and when a response to the test signal is directly received, switching to usage of a wireless direct link service is performed (Japanese Patent Application Laid-Open No. 2003-348103).
Moreover, a method is known in which a destination broadcast probe request signal is transmitted from a wireless terminal, and determination of availability of usage of a wireless direct link service is performed by studying the contents of a corresponding probe response signal (Japanese Patent Application Laid-Open No. 2003-18234).
However, in the configuration disclosed in Japanese Patent Application Laid-Open No. 2005-33536, in order to provide a wireless direct link service, it is required that a wireless access point (base station) always has accurate knowledge regarding positional relationships of wireless terminals within a system. Therefore, the base station must support such processing, and processing by the base station may become complicated.
In addition, in the methods disclosed in Japanese Patent Application Laid-Open No. 2004-128785 and Japanese Patent Application Laid-Open No. 2003-348103, it is necessary to establish a communication partner wireless terminal before confirming availability of a wireless direct link.
Furthermore, in the method disclosed in Japanese Patent Application Laid-Open No. 2003-18234, a receiving terminal of a probe request signal must send back a probe response signal even when a transmission source of the probe request signal is not a terminal performing the intended communication. Therefore, unnecessary communication traffic will increase on the network system.